<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="parent">
        <div class="test"></div>
    </div>
</body>

</html>
<style>
    .parent {
        border: 2px solid #333;
        width: 100px;
        height: 100px;
        display: flex;
        justify-content: center;
        align-items: center;
    }

    .test {
        width: 40px;
        height: 40px;
        background-color: pink;
    }
</style>